I always wondered why there is so much misunderstanding about the voltage of the 12V battery made for cars. It’s a 12-volt battery, so it should always read something about 12 volts, right? Not completely so. When it’s charged, it may read much more than 12 volts and when it’s under high load, it can read much less than that and still be OK. But what if it reads 17 volts?
In short, if your 12-volt battery reads 17 volts, something is certainly wrong, this can be the bad charger, faulty alternator, shorted battery, faulty wiring, and other issues. Usually, you shouldn’t continue using your vehicle if you notice that the battery reads 17 volts. This may lead to all kinds of different issues.
In this article, I will cover the following:
- How should you check the voltage of the battery in your car?
- Why can a car battery read 17 volts instead of the standard 12 volts?
- What can go wrong if the voltage of your battery is too high?
- What to do if you see high voltage in your car battery?
Checking the voltage of the battery – little tricks
When a person needs to check the voltage of the battery in their vehicle, they will usually take the multimeter, set it to volts, DC, and then just use the multimeter’s contacts to connect them to the battery terminals and check the voltage. This will work if the car is off. And even in this case, you may get wrong readings because something may be slowly draining the battery and the voltage will drop.
Here’s how you can get clear battery voltage:
- Make sure the vehicle is off and nothing is draining the battery.
- Take the cable off the positive terminal.
- Take the cable off the negative terminal.
- Use your multimeter to measure the voltage by connecting it to the battery terminals.
- Connect the negative terminal and then the positive terminal back to the car’s cables.
- Turn on the air conditioner without turning on the engine (just use accessory mode for this).
- Get back to the battery and measure the voltage now when it’s under some load.
This way, you will learn the clear voltage of the battery when nothing is disturbing it. In the optimal car battery, it should be around 12.5 volts. After that, you put some significant load on the car battery and then check the voltage again. It should be just a little less than before – 12.1 or maybe 11.9 volts. If it drops to 10 volts or even lower, then the battery is not completely healthy and maybe it needs some charging or even replacement.
Why is it not correct to just check the voltage of the battery when the engine is working? In this case, you will get the voltage of the alternator, not the battery. Even if the battery is dead, the alternator will still be sending some voltage to it and trying to charge it.
Why and how can a car battery read 17 volts?
Whenever you see 17 volts in your car, your best move will be to just turn off the vehicle and disconnect the battery. Your vehicle can withstand a voltage of up to 15 volts. Anything higher than that may easily fry something in the electrical system of the car. If 17 volts will be sent to ECU for example, or to some fuses, the problems will not be long to come.
But let’s first see why and how this may happen. It’s very unlikely that the battery itself reads 17 volts. At least, I haven’t seen such cases in my life. It’s likely that the cables that are connected to the battery are sending high-voltage current to the battery and are overcharging it.
Here’s why this may happen:
- there is another battery in your vehicle (hybrid) and it malfunctions heavily sending high voltage to the entire electrical system of the vehicle (though, it’s very unlikely to happen);
- the alternator is going crazy and producing a high-voltage current – this is a scary situation and you should turn off the engine immediately;
- the voltage regulator is faulty – this small part can send high or low voltage to the battery and other units in your vehicle;
- something is shorted in the system – the electrical system of your car is not eternal, something may have broken or shorted and now is causing problems.
The most obvious reasons are the problems with the alternator or the voltage regulator. But short circuits shouldn’t be overlooked. It can also damage the car’s electrical system quite badly. Unfortunately, there are no simple and straightforward ways to check the work of your alternator and/or voltage regulator, so you should go to specialists. Avoid driving your vehicle with such problems, better have it towed to the dealership or repair shop.
So, now you know that it’s most likely not the battery voltage if you find out it’s 17 volts. It means that something in your car causes heavy battery overcharging and may eventually kill it and fry something else in the vehicle.
What are the possible effects of high voltage in your car?
The majority of modern vehicles are protected from electrical problems by fuses. Once something is wrong with the current, the fuse is blown and the electricity is not supplied to certain units. This protects some of the most expensive and important units in your car, but not all.
Your ECU will still get this high-voltage current and may get fried quite quickly. Also, the voltage regulator will die almost immediately once this starts happening with the car. Another problem is that thin wires may overheat and even melt, and some connections may be quickly spoilt.
Here are the possible consequences of 17 volts in your vehicle:
- The death of the ECU. While this small part seems easily interchangeable, it’s not so in the majority of vehicles. You will spend a lot of time and money till you install the new ECU and make it work well.
- Blown fuses. This is not a really expensive problem but sometimes you will need to ask a professional car mechanic to cope with it. Locating and replacing blown fuses is not always that easy.
- Blown wires and connections. Thin wires in your car are not made to withstand 17 volts. They will overheat and maybe even lose connections. This will lead to issues with the electrical system that are hard to locate and repair.
- Glitching electronics. Any electronic unit can malfunction because of high voltage. For example, if the fuse isn’t blown, your infotainment may glitch or be damaged.
- Some light bulbs may be blown. LED lights, some sensitive small lights in your interior may be blown because of high voltage.
Also, you may see a check engine light with several random codes behind it. Some sensors may stop working, some control systems may trigger other issues. High voltage in the electrical system of your car may actually lead to irreparable damage. If several control units are broken, it will cost you a fortune to get your vehicle back on the road.
We often underestimate the problems that can happen because of the wrong voltage. But high voltage is very hazardous for your car and it can lead to unwanted consequences.
Your actions if you catch high voltage in your car
If you understand or check that your vehicle is now getting super high voltage, something like 17 volts, you should do the following:
- turn off the engine and the ignition immediately to avoid damage to expensive units;
- open the hood and locate the car battery;
- disconnect the battery (first positive, then negative terminals);
- find a way to get your car towed to the dealership or repair shop that you can trust;
- let specialists inspect the vehicle and avoid connecting the battery back on your own until you understand the reason.
Unfortunately, when it comes to the electrical system of your car, it’s very hard to locate the problem and solve it. In most cases, you will not be able to inspect the car on your own. Even skilled and experienced mechanics will need several hours to locate the problem unless it’s something obvious and common.
If your vehicle is not covered by the warranty, you may still want to go to the dealership first. They have more sophisticated tools that help them to diagnose your car’s electrical system faster and with higher precision. After you know the problem, you can get the car to any other repair shop to reduce your costs.
Final thoughts
If you find out that your car’s electrical system has very high voltage, remember that the vehicle is not safe to drive. You shouldn’t even turn on the ignition or accessory mode, in this case. 17 volts is too much for a car, so you better go to the repair shop or to the dealership immediately and find the actual reason for the problem.
You should be ready for some unpleasantly expensive repairs because the electrical system is usually quite hard to diagnose. Even locating the issue may cost you quite a lot of money. But anyway, driving a vehicle with such problems is not a good option.